Screw-propeller



NTED @TETES PATENT OFFCE,

JAMES MONTGOMERY, OF BALTIMORE, MARYLAND.

SCREW-PROPELLER.

Specieaton forming part of Letters Patent No. 23,598, dated April 12,1859; Ressued. April 22, 1878, No. 5,364.

To all whom it may concern:

Be it known that L JAMES MONTGOMERY, of the city and county of Baltimoreand State of Maryland, have invented a new and useful improvement inScrew-Propellers; and I hereby declare the following to be a full andexact description of the same, reference being` had to the accompanyingdrawings, making part of this speciiication, in which- Figure l is anend view and Fig. 2 a side elevation of a propeller embodying myimprovement. Fig. 3 is a perspective view of one blade detached from theshaft and from the surrounding cylinder.

The subject of the said invention is a screw propeller composed of twoor more blades surrounded by a cylindrical casing securely attached tothe blades at their periphery and revolving therewith.

A, is the shaft of the propeller.

B, B, are helical blades cast separately and each formed with asegmental iiange b, which fianges are made to clasp the shaft and arethere irmly secured by bands D, so as to form the hub of the screw. Thebands D, are by preference shrunk upon the hub Z9, but may be formedwith taper screwthreads adapted to fit corresponding threads formed uponthe hub b C, is a cylindrical casing surrounding the periphery of theblades and lirmly attached thereto by tenons c, and riveted as shown.rlhe chief object of this cylindrical casing is to aiford mutual supportto the ends of the blades and bind the whole structure firmly togetherin a similar manner to the tire of a carriage wheel so that a strain orshock imparted to any one of the blades is equally sustained by all. Bythis means I am enabled to produce a. propeller of much greater strengthand durability while its weight is much reduced, the support of thesurrounding cylinder enabling the blades to be made extremely light. Forthe same reason the blades meet with much less resistance in clearingthe water. The more rapid the motion of the vessel the coarser should bethe thread of the screw by which it is propelled. The Obliquity of theblades will therefore be adapted to accord with the model of the boatfor which the screw is intended.

The connection between the ends of the blades and the cylindrical casingis required to withstand a severity of strain for which rivets alonewould be entirely insufficient. The tenons c, are therefore formed inone piece with the blade and by engaging in corresponding mortises inthe casing prevent such play or motion between the two as would severand destroy the rivets. When the blades are constructed of wrought iron,the ends of t-he tenons will be upset or clenched on the outside of thecasing but with a cast blade the tenons will be made in dovetail formand secured in the casing by calking or wedging from the outside. Thecylindrical casing likewise serves to protect the blades of the screwfrom contact with canal banks, tow lines, drift wood, water grasses, andother matters which produce serious inconvenience in various ways wellknown to those engaged in canal navigation and acquainted with the useof the screw propeller; and is also beneficial in arresting thetangential motion of the water which involves much loss of power andproduces disastrous effects upon the banks of canals and other narrowwaters.

It is well known that in the early period of the application of thescrew to the propulsion of vessels it was proposed to employ a form ofscrew similar to that invented by Archimedes for raising water, whichconsists of a spiral chamber coiled around an axis and open only at theends. This was early superseded by a. simple continuous spiral flangewhich possessed the advantage of admitting water more freely to itsaction. Subsequently the more perfect propeller of the present day wasintroduced which consists of a plurality of blades attached to a shaftin substantially one plane. This form of screw is found eiiicient anduseful in its application to sea going vessels but the continuity of thespiral throughout its circumference being broken it is found necessaryto make the blades extremely strong and massive and they arenotwithstanding frequently broken by violent concussions of the sea oragainst solid bodies. The weakness of the stern frames of vessels ascustomarily constructed and the location of the screw propeller at theextreme stern (and sometimes without any outside bearing) render theweight of such a screw a serious inconvenience sometimes attended withdisastrous consequences.

In some applications of the screw propeller, and particularly in thenavigation of canals and other small bodies of water in which the motionof the screw is comparatively slow much loss of power is experiencedfrom the resistance which water offers to the rotation of a screw whoseblades are of such thickness as has hitherto been found essential tostrength. I have accordingly devised a method of applying an exteriorcylindrical casing to a screw composed of a plurality of blades andattaching it in such a manner to the peripheries of the said blades thatany sudden or excessive strain on either of the blades is sustained bythe said cylindrical casing and by it distributed equally over theentire structure7 the said casing serving also the combined purposes ofpreserving the blades from contact with passing objects and arrestingthe tangential motion of the Water which involves loss of power andcauses serious injury to canal banks.

I claim as new and of my invention and desire to secure by LettersPatent.

A screw-propeller composed of a plurality of blades attached to theirshaft in one plane or nearly so, when surrounded by a containingcylinder rmly attached to the peripheries of the said bladessubstantially in the manner and for the purposes set forth.

In testimony of which invention, I hereunto set my hand.V

JAMES MONTGOMERY.

W'itnesses OCTS. KNIGHT, EDM. F. BROWN.

